Electric and hybrid vehicles may have one or more voltage buses (e.g., high voltage buses) that are isolated from the ground and chassis reference of the vehicle during normal operation. However, if an electrical short or another electrical problem occurs in vehicle circuitry or electromechanical devices (e.g., motors or generators), one or more voltage buses may apply or leak undesired electrical energy to the chassis of the vehicle or vehicle electronics, which can detract from vehicle performance or reliability. The level of observed leakage current may vary over an extensive range depending upon the particular facts and circumstances related to the electrical short or other electrical problem. To accommodate the extensive range of possible observed leakage current, certain prior art approaches can result in costly, bulky or complicated circuitry to accurately measure isolation between the voltage bus and the chassis. Thus, there is need to detect degraded electrical isolation between one or more voltage buses and the chassis of the vehicle over an extended range of possible observed leakage current without undue cost, bulkiness or complication.